1. Field of the Invention
The present invention relates to a method for manufacturing a module type electronic component which can increase the adhesion strength of a cover attached to the electronic component and minimize variations in the adhesion strength.
2. Description of the Related Art
Recently, radio communication devices such as mobile phones have become popular, and module type electronic components like the one shown in FIGS. 15A to 15C have been commonly used to reduce the size, weight, and cost of the radio communication devices and to ensure their resistance to change over time and functional stability. The electronic component shown in FIGS. 15A to 15C includes a circuit board 52 on which mounting elements 50 such as IC chips, capacitors, resistances, and coils are surface-mounted and a metal cover 54 which is attached to the circuit board 52 such that the mounting elements 50 are covered with the metal cover 54.
A method for manufacturing the above-described electronic component will be described below. First, as shown in FIG. 15B, through holes 52a which are formed in the rectangular plate-shaped circuit board 52 such that they extend through the thickness of the circuit board 52 at the periphery thereof are filled with solder cream 56. In addition, as shown in FIG. 15A, tabs 54a are provided on the open side of the box-shaped metal cover 54 at positions corresponding to the through holes 52a. Then, as shown in FIG. 15C, the tabs 54a are inserted into their respective through holes 52a so that the mounting parts 50 are covered with the metal cover 54. Then, the solder cream 56 disposed in the through holes 52a is melted by heating and solidified so that a solder member 56a is obtained. Accordingly, the metal cover 54 is attached to the circuit board 52 and the manufacturing process of the electronic component is completed.
With reference to FIG. 16, in order to fill the through holes 52a with the solder cream 56 in the above-described manufacturing method, a print mask 58 is disposed on the front surface of the circuit board 52 and the solder cream 56 is supplied to the through holes 52a through openings 58a formed in the print mask 58 by printing using a squeegee 60.
In this method, recesses 58b for receiving the mounting elements 50 must be formed in the print mask 58 so that the mounting elements 50 placed on the front surface of the circuit board 52 can be prevented from being damaged. Therefore, the thickness of the print mask 58 increases by the amount corresponding to the heights of the mounting elements 50, and the dimension of the openings 58a along the thickness of the print mask 58 increases accordingly. As a result, a large amount of solder cream 56 is used and costs are increased.
In order to overcome the above-described disadvantage, according to Japanese Patent No. 2850860 (disclosed on Jan. 16, 1998), a print mask is disposed on the back surface of a circuit board having mounting elements on the front surface thereof, and solder cream is supplied to the through holes through the print mask by printing. Then, tabs of a cover are inserted into the through holes and are attached to the through holes with solder. Accordingly, the thickness of the print mask can be reduced.
In FIG. 16, in order to increase the productivity (to reduce costs) of the electronic component, a large wafer including a plurality of circuit boards 52 is used. The metal cover 54 is attached to each of the circuit boards 52, as shown in FIG. 17A, and then a plurality of electronic components are manufactured by separating the circuit boards 52 from each other along cutting lines (imaginary lines) which pass through the through holes 52a by, for example, dicing.
Other examples of known methods are disclosed in, for example, Japanese Unexamined Patent Application Publications No. 6-305272, No. 8-250855, and No. 2001-196733.
According to the above-described known method, when the solder cream 56 is supplied to the through holes 52a as shown in FIG. 17A, and is melted and solidified so as to obtain the solder member 56a and achieve adhesion as shown in FIG. 17B, excess solder 56a may come into contact with terminals of the mounting elements 50 placed on the circuit board 52. In such a case, the electrical characteristics of the mounting elements 50 are degraded due to short circuit or other defects and malfunction occurs in the mounting elements 50. Therefore, the yield of the electronic component is reduced.
More specifically, in the above-described known method, a single through hole 52a receives two tabs 54a, one belonging to each of the adjacent metal covers 54, and the size of each through hole 52a is large since a predetermined interval must be provided between the adjacent metal covers 54 in order to attach them. Accordingly, a large amount of solder cream 56 is used for filling each of the through holes 52a. 
When such a large amount of solder cream 56 is melted for adhesion, excess molten solder cream 56 comes into contact with the terminals of the mounting elements 50 placed on the circuit board 52, as shown in FIG. 17B. Then, when the solder member 56a is obtained by solidifying the solder cream 56, the mounting elements 50 are electrically connected to the metal covers 54, which are normally short-circuited (grounded). Therefore, malfunction due to short-circuit occurs and the yield of the electronic component is reduced.